There is a clear disproportion among catalogued SySt in favor of the burn-SySt type, and the known examples of the acc-SySt variety are
believed to be just the tip of the iceberg ([1]},
hereafter Mk16). Between 15 and 20 are currently known of the acc-SySt type. Symbiotic stars were originally proposed by
[2]} as possible progenitors of type Ia supernovae,
and the viability of this single-degenerate channel obviously relies on the
total number of SySt spread throughout the Galaxy, which in turn heavily
depends on the number of acc-SySt. The latter have been usually
discovered as counterparts of satellite UV/X-ray sources, while the burn-SySt can be easily spotted at optical wavelengths through the whole
Galaxy and the Local Group thanks to their outstanding emission-line
spectrum (with ionization up to [FeX] and beyond).
